The battery of the future: Scientists investigate extremely fast ion conductors


id31611(Nanowerk News) Only since April of this year have  experts been researching batteries of the future at the Christian-Doppler (CD)  Laboratory for lithium batteries at the Institute of Chemistry and Technology of  Materials of Graz University of Technology – and they are already attracting  attention with their pioneering results. Using detailed magnetic resonance  measurements, they were able to prove the ultra-fast lithium ion dynamics of a  superb conductor being suitable, e.g., for solid-state batteries. Solid-sate  lithium-ion batteries are the great white hope in terms of storage capacity,  durability and safety. The results of the doctoral thesis of Viktor Epp were  recently published in the prestigious Journal of Physical Chemistry  Letters (“Highly Mobile Ions: Low Temperature NMR Directly  Probes Extremely Fast Li+ Hopping in Argyrodite-type Li6PSe5Br”).
Not only the sustainability of the success of electro-mobility,  but also the development of high-performance cell phones and notebooks make high  demands on battery systems. Higher storage capacities, safety and  ever-increasing durability are some of the demands they have to live up to.  Solid-state lithium-ion batteries are one of the great white hopes in battery  research. Compared to conventional lithium-ion batteries with liquid  electrolytes, these so-called “all-solid-state“ batteries are ahead of the game  as regards safety, operational life span and thermal stability. For this reason,  researchers all over the world in the fields of solid-state chemistry, physics  and materials science have been under pressure to find suitable, solid-state ion  conductors for use in such batteries.
In his doctoral thesis, Viktor Epp, from Graz University of  Technology’s Institute of Chemistry and Technology of Materials, looked more  closely at the sulphide Li6PSe5Br  which was prepared in the well-known working group of Hans-Jörg Deiseroth at the  University of Siegen. Using lithium nuclear magnetic resonance spectroscopy, as  it is carried out in the CD Laboratory in Martin Wilkening’s group, he came to a  remarkable result which confirmed earlier preliminary work: the lithium ions in  the investigated sulphide move extremely quickly. This qualifies Li6PS5Br as a  front runner among solid-state electrolytes which could be used in solid-state  batteries.
“Hopping” atoms: a billion jumps per second
The observed “hopping process” of the lithium ions in Li6PS5Br  have proved to be remarkable. With ambient-temperature rates of more than one  billion jumps per second, the ions in the investigated sulphide show an  extremely high mobility. Such mobility has also been shown in other lithium  compounds, however, many of the materials are not only ionically but also  electronically conductive – and can thus be excluded as solid-state  electrolytes. At first glance, the basic principle of electrochemical energy  storage in a lithium-ion battery is relatively easily to understand. During  charging and discharging of the battery, the ions move between both poles, thus  passing through structurally different materials. In the case of a solid-state  lithium-ion battery, a solid, such as a lithium-containing oxide or a sulphide,  takes on the role of a conductive electrolyte.
“The more we know about the nature of the charge carrier  transport in solids, the more evident it will become, which materials are most  suitably for the future development of batteries“, explains Martin Wilkening,  who, along with his team in the CD Laboratory, is dedicated to the investigation  of microstructures and dynamic processes in new battery materials.
Source: Technical University Graz

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